Create service-connectivity.jar

Create a new target service-connectivity to split
ConnectivityService from services.core.

Add ConnectivityServiceInitializer for initializing
ConnectivityService and add systemReady() in
ConnectivityManager so that SystemServer can call systemReady()
through ConnectivityManager which won't change current behavior.

Bug: 158268939
Test: make target-java, make host-java
      atest FrameworksNetIntegrationTests
      atest FrameworksNetTests
      make, device can boot,
      atest CtsStrictJavaPackagesTestCases
      wifi and mobile data work.
Change-Id: I99401772ba9c1c34adca20040da3c7c72d86ddd9
Merged-In: Ie732bfaf381404af0bb599ca2f421a96e7aa4257

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -1246,7 +1246,7 @@ public class ConnectivityServiceTest {
         // Create local CM before sending system ready so that we can answer
         // getSystemService() correctly.
         mCm = new WrappedConnectivityManager(InstrumentationRegistry.getContext(), mService);
-        mService.systemReady();
+        mService.systemReadyInternal();
         mockVpn(Process.myUid());
         mCm.bindProcessToNetwork(null);